This coin is from the 9th workshop, but rather than use Θ (theta), which is Greek for nine, the engraver used delta (Greek for 4) and epsilon (Greek for 5) which add up to nine. Theta was considered by some to be the symbol of death, so it was best to avoid using it.
There are other examples of this practice, however, on some LRB’s, Θ is used to denote a workshop, so perhaps there was an overly superstitious supervisor at Antioch during this period.
The second picture (courtesy of wikipedia) shows a mosaic from the Villa Borghese in which dead gladiators have a symbol (a sloppy theta) below their names to show that they are dead.
Constantine I
A.D. 327- 328
18x19mm 3.2gm
CONSTAN-TINVS AVG; head with rosette diadem.
PROVIDEN-TIAE AVGG; camp gate with two turrets and star between them, in left delta and right epsilon.
in ex. SMANTE
RIC VII Antioch 78